There's an article in New Scientist about using sound waves to propel space craft.
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The actual article is discussing the Sterling Engine converter for the Radio-isotope thermo-electric motors. There have been a few threads about this over the last year. Essentially, it is saying that the current thermocouple approach to getting power is about seven percent efficient, whereas the Sterling engine approach is already at eighteen percent and could soon get up to twenty-five percent.

This might be an important technology for the next ten years or so, and for small probes that won't be able to use the Promethius platform's fission reactor. It will be interesting to see if they get it working fast enough to use it on the Mars 2009 Rovers.

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That's interesting!

Speaking of nuclear energy, nuclear propulsion in space crafts is very efficient but at the same time can be so dangerous. I mean if any other accidents occur just, like sad one of Columbia, then the rocket will become a live nuclear bomb.

I don't know if it's worth the risk! What do u think?

I think great care has to be used designing such power systems so that no catostropic accident will result in run-away fission, or even a large scale release of deadly chemicals, such as oxides of Plutonium.

As it happens, great care about such things is taken.

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What a hoot that one note was that this sound machine could produce propusion energy for submarines. It would give a new sense of irony to the call to "rig for silent running!"